Method for producing bicomponent polypropylene filaments



ABSTRACT. on THE DISCLOSURE Self-crimping bicomponent polypropylene filaments are made by conjugate melt spinning two different polypropylene polymers in side-by-side or sheath-core relationship and subsequently relaxing the filaments. The polymers have the same intrinsic viscosity but different molecularwe ght distributions. Enhanced crimp is effected by drawmg the filaments.

DISCLOSURE This invention relates to a process for the production of self-crimping polypropylene filaments or filamentary yarn.

It is known, from British patent specification No. 805,- 033 to produce filaments from at least two chemically different synthetic polymers by a melt-spinning process wherein the molten polymers are fed separately to the mers distributed non-uniformly across the cross-sections vof the filaments, the non-uniformity giving rise to an inherent crimping potentiality in the filaments.

It is also known, from British patent specification No.

States Patent shaping orifices and form filaments having the two poly- 979,083 to produce spontaneously crimping polyolefine filaments from two polyolefine components of different viscosity arranged in side-by-side relationship .along the length of the filaments.

We have now found that self-crimping polypropylene filaments or filamentaryyarn may be produced without this viscosity difference or with a substantially reduced viscosity difference between the two polypropylene components. t

According to the present invention we provide a process for the production of self-crimping polypropylene filament-s wherein composite filaments having two different propylene polymers distributed along the length of the filaments as distinct components in side-by-side or sheathcore relationship are produced by conjugate melt spinning coefficient, Q, .as hereinafter defined, of at least 6.5 and :thatthe diiference between the Q values of the components should be at least.0.5 for an adequate crimpingeifect to be obtained...

Filaments or filamentary yarn according to the invention are described as self-crimping for upon release of the tension applied to them during melt-spinning or the subsequent .cold-drawing. steplthey contract and take-up a helically crimped form. The tension may be maintained in the filaments between and subsequent to these processes .by, for example, winding the filaments or filamentary yarn on to bobbins and then released at an appropriate stage in the subsequent textile processing. Thus, self-crirnped staple fibres may be produced bygcutting an uncrimped yarn or tow into staple lengths while allowing relaxation to take place. Alternatively the filamentary yarn may be subjected to a mechanical crimping process before releas- 3,399,259 Patented Ang. 27, less ice ing the tension to impede the self-crimping effect sufficiently to facilitate subsequent textile proeessir ig.v

The substantial absencev of mechanical restraint during relaxation will lead to the maximum crimping effect. However in some uses to which the crimp'ed fibres or filaments are put it is desirable to control .the extent of crimping achieved as the maximum crimping effect may lead ,to'a'n undesirable harshness of handle in thelresultan't yarnor fabric.

Although self-crimping filaments or filamentaryv yarns produced as in this invention may show theself-crimping effect in the as-spun condition, the effect is much enhanced by drawing the as-spun filaments, preferably tomore than twice but not more than about four times their original length at a temperature not exceeding about C.

We have found that the degree of crimping -effect obtained upon relaxation may be controlled independently of the composition of the composite fibres by. regulating the temperature of the snubbing surface '(pin or roll) upon which drawing is effected. As the temperature'of the snubbing surface is increased so the crimping effect obtained is decreased until at about 100 C. little crimping is achieved. Thus, for example by drawing composite filaments, the components of which have dispersion coefficients of 8.4 and 4.7 andthe same viscosity, 1.55, at a draw ratio of 3.521 we obtained the following results for percentage crimp under a load of 0.5 mg./denier as the temperature of the snubbing surface, in this case a heated feed roll, was increased.

It is preferred to stabilise the helical form of the selfcrimped fibres by a heat treatment in the relaxed state at a temperature of about 100-140" C Some increase of the self-crimping effect may accompany stabilisation of the crimp by the heat treatment.

Several forms of melt-spinning apparatus for conjugate spinning of side-by-side or sheath-core composite filaments are known, as for example, British patent specifications 953,379 and 972,932 and such equipment may be used to form composite polypropylene filaments according to the invention. The terms side-by-side and sheath-core refer to the relationship of the two components in the individual filaments and the term conjugate spinning refers to the production of such composite filaments.

The dispersion coefficient, Q, which is an expression of the molecular weight distribution of a propylene polymer, is the ratio of weight average molecular weight, MW, to number average molecular weight, fin. We have determined the Q values of propylene polymers comprising the conjugate filaments from measurements of lVw and fin by, respectively, light scattering and membrane osmometry techniques which are described in detail hereinafter, using the component polymers as supplied to the conjugate melt spinning apparatus as it is impossible to separate the components of the spun conjugate filaments. Control tests wherein individual propylene polymers are melt spun under conditions identical to those used in the conjugate melt spinning process show that do degradation or change in viscosity or molecular weight distribution. is

incurred during melt spinning.

DETERMINATION OF MW For this determination we have used a photo-gonio diffusometer Model 42,000 of the Societe Francaisdlnstruments de Control et dAnalyse (SOFICA). g

Light scattering measurements were carried out at using unpolarised light of wave-length 5461 A., the

"light scattering cells beirig immersed in a temperatur e conblank used in each measurement were carefully clarified by filtering at 130 C. through a sintered glass filter, to remove all traces of dust etc. 7 I

7 Ten ml. portions of the clean polymer solutions and the solvent blanks were used, measurements being taken at scattering angles of 30150 (in eleven steps) to the incident beam. Between the measurements for each solution the intensity of the incident beam of light was checked for constancy against the reading at 90 for a standard diffusor.

, The instrument was calibrated with benzene and the instrument constant checked against a standard polystyrene specimen of known molecular weight (National Bureau of Standards No. 706, Hw=258,000). The molecular weight of the standard was calculated using the accepted value of the Rayleigh ratio of benzene, 163x10 and YlTw was found to be 256,000. Benzene was thereafter used as a standard for converting the photomultiplier reading to the absolute scattering intensity by the equation where R, is the Rayleigh ratio of the solution (corrected for solvent scattering) at any angle 0, R is the Rayleigh ratio of pure benzene, I, is the instrument galvanometer deflection forthe solution in excess of that of the solvent, 1,, is the galvanometer reading for pure benzene,

is the square of the ratio of the refractive indices of the solution to that of benzene. Sin and (l-l-cos 0) are cor- -mometer made by Dohrman Instrument Co. to a Shell rection factors for the volume of scattering at angle 0 and the use of unpolarised light respectively.

The usual light scattering equation is N=Avogadros Number and sin 0 a 1 cos 0 Using the accepted values for the constants we have For polypropylene in a-chloronaphthalene at 130 C. and

=5461 A., d /dC=-0.189 mL/gm. Using this and set- 'In accordance with the last 4i 1 ting I ,-=l.3 2 I (where I is thescattering intensity of the standard diffusor) we have V II equation Zimm plots were obtained by plotting i against (sin 20/ |-.50 C.). The term 50 C. is a geometric one to give a good spread of the 55 points contained in each Zimm plot. The extrapolated lines 0:0 and 0:0 should intercept the ordinate at the same point le O=0 DETERMINATION OF fin For this determination we have used a high speed os- Development Corporation design, equipped with an ultracella allerfeinst? membrane made by 'Membranfilter Gesellschaft, Gottingen.

The membrane was conditioned by immersion for not less than 6 hours in the following sequence of solvent mixtures; water, water/ethanol, ethanol, ethanol/ acetone, acetone, acetone/methyl ethyl ketone (MEK) MEK, MEK/ toluene, toluene, toluene/decalin and decalin. The membrane was then conditioned for high temperatures by first of all securing it in position is the osmometer and filling the solvent and solution compartments with solvent. The temperature in the osmometer was then raised by 30 C. stepsuntil a temperature of C. was reached allowing 8 hours conditioning at each temperature. The solvent used for the measurements, decalin, was vacuum distilled prior to use and oxidation was inhibited 'by the addition of 0.1% w./v. of a phenolic antioxidant.

Polymer solutions (with a concentration chosen so as to give a pressure head of at least 1.2 cm. of solvent) were prepared at C. in pre-calibrated volumetric flasks and the solutions so prepared were filtered, prior to injection into the osmometer, at 130 C. through two thicknesses of 0.8 Millipore membrane filters (Millipore Corporation of America). The injected solutions were allowed 5 minutes to equilibrate in a 'pre-heater in the osmometer before being allowed to enter the solution compartment wherein a further 10 minutes'equilibration time was allowed. I

The instrument zero was established by repeatedly filling the solution compartment with solvent and measuring the pressure head each time on the manometer servo read-out dial, the instrument zero being taken as satis factory when three readings agreed to within $0.01 cm. of solvent. The sample outlet was then closed and the equilibrium pressure reading was taken after about 40 minutes. The process was then repeated for another portion of the same solution, whereafter the instrument zero Was re-established in the foregoing manner. As solute diffusion was always found to be present, the initial and final instrument values did not agree and the diiference in these readings was used to correct the final solution concentration reading for diffusion. j I

,The pressure readings obtained from 'this instrument are for the solvent at approximately 20-25 C., therefore the osmotic pressure 1r is given by (h-h0) Where h0=solvent zero in cms. h=solution zero in cms. p=density of solvent at 25 C.

The osmotic pressure readings obtained are then plotted as 1r/ c against C, where C is the concentration of where R is the gas constant and T is the absolute temperature.

For many purposes a shortened method of measurement is quite satisfactory. Thus instead of measuring the osmotic pressure for a number of polymer solutions of different concentrations and extrapolating the results to zero concentration we have used a single very dilute solution measurement and used this value as a close approximation for (1r/C) C=0 as we have found that the values so obtained agree with the values by extrapolation of a number of polymer solutions within 3%. Values obtained by the shortened method were therefore increased by a factor of 3% to give a close estimate of fin. The accuracy of determination is approximately $750 molecular weight units.

Polymers having different molecular weight distributions may be produced in several ways. Thus thermal degradation of polypropylene from a higher to a lower viscosity will cause a narrowing of the molecular weight distribution, the product then being used as one component of a composite filament, the other component being, for example, a polymer which has been subjected to a lower degree of degradation. Alternatively a polymer manner in which it may be performed. As the force with which self crimping occurs has an effect upon the degree of crimping attained we give in these examples the degree of crimp achieved by (a) substantially free relaxation (0.01 mg./denier) and (b) under a load of 0.5 mg./denier, which is the order of the resistance to relaxation in a loosely twisted multifilamentary or staple fibre yarn such as would be used for example for hand knitting purposes. In order to measure the crimping effect under a specified load we wind small hanks (100 cm. long) of filamentary yarn around a 10 cm. Perspex (Regd. Trade Mark) rectangular former, remove the hanks, suspend therefrom an appropriate lead, heat treat in an air oven for 10 minutes at 135 C. and then measure the contracted length of the unwound hank with the load removed (L and thelength (L of the unwound hank with the crimps just removed by extension. The percentage crimp obtained is then expressed as EXAMPLES 1-7 Conjugate melt spinning apparatus, having means for separately supplying two molten polymers to a spinneret at independently controllable rates, is used to produce composite filaments from seven pairs of propylene polymers each pair having the same intrinsic viscosity but different molecular weight distribution and equal proportions of each component. The component polymers join at the spinneret orifices to produce composite filaments of the side-by-side type. The spinnerets used have 24 to 60 orifices of 0.020 inch (0.051 cm.) diameter as noted hereinafter and in all cases except two (Examples 6 and 8) the denier per filaments of the spun filamentary yarns was 15. In Examples 6 and 8 the spun denier per filament was 20. Other spinning conditions and additive substances present in the polymers are given in the following table.

Example No. Intrinsic Q, values No. of Spinneret Wind-up speed Additives viscosity orifices temp., C m./min.

1. 1 8. 4/3. 7 36 204 457 None. 1. 3 8. 4/4. 65 36 205 457 10% polyamide and delustrant. 1. 3 8. 4/6. 3 60 206 274 0.1% phenolic antioxidant. 1. 3 7.0/4. 65 36 205 457 10% polyamide and delustrant. 1. 55 8. 4/7. 7 36 205 366 None. 1. 55 7. 7/4. 7 24 203 655 10% polyamide. 1. 8 8. 4/5. 1 48 206 195 10% polyamide and delustrant.

which has been chain terminated during polymerisation, as for example by the use of hydrogen as chain terminator, and which has a broad molecular weight distribution, may be used as the second component. The proportion of a particular component in the composite filament may be varied between about 1:9 to 9:1 the selfcrimping effect obtained over this range being somewhat dependent upon the difference between the Q values for each component. Thus if the Q value difference is high the proportion of the components may differ more from 1:1 than for small Q value differences.

Component polymers may contain up to about 20% by weight of other substances, as for example, stabilising substances, delustrants or pigments or substances conferring an aflinity for dyestuffs on the propylene polymers.

Where the term viscosity is referred to herein, in relation to the process of the invention, intrinsic viscosity measured in decalin solution at 135 C. using a viscometer capillary diameter of 0.44 mm. is meant; the units of viscosity being decilitres/ gram.

In selecting suitable propylene polymers for use in the preparation of composite filaments according to the invention, we prefer to use polymers which, in addition to having a difference between the Q values of a selected pair of at least about 0.5, also have an intrinsic viscosity of not less than 1.0, as little or no self crimping effect is obtained with polymers of lower viscosity, particularly if the difference in Q value for the pair is low.

The following examples illustrate the invention and the All percentages are by weight of the polymer composition.

The spun yarns were collected on rigid bobbins and drawn using a heated feed roll, whereon drawing took place, drawing apparatus with a draw roll temperature of 20 C. or C. In all examples except No. 5 a draw ratio of 3.521 was applied and in the case of Example 5 a draw ratio of 3.0:1 was applied. The feed roll in all cases was maintained at 55 C.

The properties of the drawn yarns made into 100 cm. hanks and treated as hereinbefore described are given in the following table together with the draw roll temperature used.

Example Draw roll temp, Percent crimp at a load of 0.01 rug/denier 0.5 rug/denier Comparative example A For comparison a 1.1 composite filament was spun using the apparatus of the foregoing Examples 1-7 and a pair of propylene polymers of Q values 5.9 and 4.65. A 36 hole (0.051 cm. diameter) spinneret maintained at 205 C. was used and the spun yarn was collected on bobbins at 457 metres/minute. The polymers were of intrinsic viscosity 1.3 and contained of a polyamide to enhance dye affinity. The spun filaments each having a denier of were drawn using a hot feed roll at 55 C.

and a cold draw roll with a draw ratio of 3.5: 1.

Upon hot relaxation of the drawn yarn no crimp was formed.

EXAMPLES 8-14 Composite filaments having varying proportions of the two components in side-by-side relationship were spun and drawn with apparatus as used in Examples 1-7, the proportions of the two components being controlled by varying the rate of supply of the molten components to the spinneret orifices while maintaining a constant spun denier per filament of 15. The propylene polymers used had Q values of 8.4 and 4.65, an intrinsic viscosity of 1.3 and contained 0.5% of calcium stearate and 10% of a polyamide. Spinning was carried out at 205 C. through a 36 hole (0.051 cm. diameter) spinneret the spun filaments being collected at 343 metres/minute and afterwards drawn with a draw ratio of 3.5 :1 using feed and draw rolls heated to temperatures of 55 C. and 100 C. respectively. The percentage crimp of the products made in this way are shown in the following table together with the proportions of component polymers used. Component A is that having Q=4.65 and for component B,Q=8.4.

Exlalmple Ratio A:B Percent crimp at a load oi 0.01 mg./denier 0.5 rug/denier Comparative example B For further comparison a 1:1 composite filament was produced using the apparatus of Examples 1-7 and a pair of propylene polymers having Q values close to the values of the components used in Example 7 but differing in intrinsic viscosity. Thus one component had a Q value of 8.4 and an intrinsic viscosity of 2.1 and the other component had a Q value of 5.2 and an intrinsic viscosity of 1.8. When spun and drawn as in Example 7 this pair of polymers produced a filamentary yarn having a percentage crimp under a load of 0.5 mg./denier of 64%.

What I claim is:

1. A process for the production of self-crimping polypropylene filaments wherein composite filaments having two propylene polymers distributed along the length of the filaments as distinct components in side-by-side or sheath-core relationship are produced by conjugate melt spinning of two propylene polymers followed subsequently by relaxation of tension in the filaments, characterized in that the two polymers have substantially the same intrinsic viscosity, but different molecular weight distributions and wherein the dispersion coefilcient, defined as the ratio of weight average molecular weight to number average molecular weight, of at least one of the polymers is at least 6.5.

2. A process according to claim 1 wherein the dispersion coefficients of the component polymers difier by at least 0.5.

3. A process according to claim 1 wherein the component polymers have an intrinsic viscosity of at least 1.0.

4. A process according to claim 1 wherein the ratio of the components is between 1:9 and 9: 1.

5. A process according to claim 1 wherein the unre-. laxed spun filaments are drawn 2 4 times their original length.

6. A process according to claim 5 wherein the drawing is elfected upon a snubbing surface heated to a temperature not greater than C.

7. A proces according to claim5 wherein the drawn filaments are heat treated on a draw roll heated to a temperature up to 100 C.

8. A process according to claim 5 wherein the crimped filaments are stabilised by heat treatment at 100-140" C.

References Cited UNITED STATES PATENTS 3,161,914 12/1964 Bloomfield et al. 264-l71 X 3,209,402 10/1965 Riley et a1. 188 3,225,534 12/1965 Knope 5714 3,264,390 8/1966 Tanner 264-171 FOREIGN PATENTS 969,110 9/1964 Great Britain.

JULIUS FROME, Primary Examiner.

J. H. WOO, Assistant Examiner. 

